A brief version of the tale appeared under the title Thinking One Can in 1906, in Wellspring for Young People, a Sunday school publication.[3] This version reappeared in a 1910 book, Foundation Stones of Success.[3]

Another version was published under the name "The Pony Engine" in the Kindergarten Review in 1910, written by Mary C. Jacobs.[3] A different version with the same title appeared in a magazine for children in 1916 under the name of Mabel C. Bragg, a teacher, but she "took no credit for originating the story".[3]

The story first appeared in print with the title The Little Engine That Could in 1920, collected in Volume I of My Book House, a set of books sold in the U.S. by door-to-door salespersons.[3] The Book House version began, "Once there was a Train-of-Cars; she was flying across the country with a load of Christmas toys for the children who lived on the other side of the mountain."[3] The story was labeled [4] "As told by Olive Beaupré Miller"; the first edition gave credit to Bragg, but subsequent editions did not as Miller subsequently concluded that "the story belonged to the
realm of folk literature".[3] Miller was the founding editor and publisher of The Book House for Children, a company based in Chicago.

The best known incarnation of the story The Little Engine That Could was written by "Watty Piper", a pen name of Arnold Munk, who was the owner of the publishing firm Platt & Munk. Arnold Munk was born in Hungary, and as a child, moved with his family to the United States, settling in Chicago. Later he moved to New York. Platt & Munk's offices were at 200 Fifth Avenue until 1957 when Arnold Munk died. Arnold Munk used the name Watty Piper as both an author of children's books and as the editor of many of the books that Platt & Munk published. He personally hired Lois Lenski to illustrate the book. This retelling of the tale The Pony Engine appeared in 1930, with a title page that stated: "Retold by Watty Piper from The Pony Engine by Mabel C. Bragg's copyrighted by George H. Doran and Co."[3]

In 1954, Platt & Munk published another version of The Little Engine That Could, with slightly revised language and new, more colorful illustrations by George and Doris Hauman.[5] Although there had been many previous editions of this classic story, "It was the work of George and Doris Hauman that earned The Little Engine the title of being worthy to sit on the same shelf as Alice's Adventures in Wonderland."[5] A 1976 rework featured art by Ruth Sanderson received a lot of attention at the time of its release, in part because the art reflected "the stereotypes of masculine strength and feminine weakness in vogue when it was written".[5]

In the tale, a long train must be pulled over a high mountain after its engine breaks down. Larger engines, treated anthropomorphically, are asked to pull the train; for various reasons they refuse. The request is sent to a small engine, who agrees to try. The engine succeeds in pulling the train over the mountain while repeating its motto: "I-think-I-can".

The story of the little engine has been told and retold many times. The underlying theme is the same — a stranded train is unable to find an engine willing to take it on over difficult terrain to its destination. Only the little blue engine is willing to try and, while repeating the mantra "I think I can, I think I can", overcomes a seemingly impossible task.

An early version goes as follows:

A little railroad engine was employed about a station yard for such work as it was built for, pulling a few cars on and off the switches. One morning it was waiting for the next call when a long train of freight-cars asked a large engine in the roundhouse to take it over the hill. "I can't; that is too much a pull for me", said the great engine built for hard work. Then the train asked another engine, and another, only to hear excuses and be refused. In desperation, the train asked the little switch engine to draw it up the grade and down on the other side. "I think I can", puffed the little locomotive, and put itself in front of the great heavy train. As it went on the little engine kept bravely puffing faster and faster, "I think I can, I think I can, I think I can."

As it neared the top of the grade, which had so discouraged the larger engines, it went more slowly. However, it still kept saying, "I—think—I—can, I—think—I—can." It reached the top by drawing on bravery and then went on down the grade, congratulating itself by saying, "I thought I could, I thought I could."

A Disney version of the story was published in 1976:

The story begins with a toy-filled train pulled by a small red engine on its way to a town on the other side of a mountain but the engine shortly breaks down upon reaching the mountain. The toy clown flags down other engines to help them: a shiny yellow passenger engine, a big black freight engine, and a rusty old engine. The shiny passenger engine and big freight engine both refuse to help them and the rusty old engine is too tired and must rest. Finally, a little blue engine arrives. Although she is simply a switcher engine and has never been over the mountain, she agrees to help pull the train. In the end, she was able to successfully reach the top of the mountain before slowly heading down towards the town.

Later versions would revamp the story to have a more specific appeal for children – the stranded train is recast as a train of good food and anthropomorphic toys for the children across the mountain, thus in saving the train the little engine seems to be working for the benefit of the child reader, making the successful deed all the more triumphant.

In these versions another character appeared and remained a key part of the story hereafter – the clown ringleader of the toys who attempts to find help with several locomotives but is rebuffed. The number of engines in the story also eventually became standard across the tellings: The happy locomotive on the toy train who breaks down and cannot go on, the pompous passenger engine who considers himself too grand for the task, the powerful freight engine who views himself as too important, and the elderly engine who lacks either the strength or determination to help the toys. The little blue engine always appears last and, although perhaps reluctant (some editions have the engine clarify her role as a switcher not suited for excursions), always rises to the occasion and saves the day for the children over the mountain.

Each engine is defined by its appearance or function and is not given a name or personality beyond its role on the railroad. It is only in the 1991 film adaption that the engines' personalities are expanded on, including the granting of names: Farnsworth (the express engine), Pete (the freight engine), Georgia (the friendly engine of the toy train), Jebediah (the elderly engine) and Tillie, the titular "little engine that could". The clown was also named "Rollo" and a sixth engine character, Doc, appeared briefly to recover the broken-down Georgia and thus tie up the hanging story-thread of what happened to the failed engine of the toy train, which all other versions leave unaddressed.

The tale with its easy-to-grasp moral has become a classic children's story and was adapted in January 1991 as a 30-minute animated film produced in Wales and co-financed in Wales and the United States. The film named the famous little engine Tillie and expanded the narrative into a larger story of self-discovery.

A full-size replica of the Little Engine That Could made an annual circuit around the United States. Arranged through Rail Events, Inc., a number of tourist and museum railroad operations hosted the "I Think I Can" Rail Tour.[7] The replica was constructed in 2005 by the Strasburg Rail Road in southeast Pennsylvania who also constructed the Thomas The Tank Engine replicas that tour the United States. The last tour was in 2008[8]. In 2009, the replica only appeared at the Texas State Railroad[9]. In 2011, the website for the tour said that there would be dates announced for 2011[10], but dates were never posted and the message was still present in 2012 until it went offline.[11] The last time the train ever operated was on September 16, 2012[12] As of 2015, the replica is owned by the Great Smokey Mountains Railroad, and has since been repainted and currently displayed at the depot.[13] Reasons for why the tour stopped are unknown.